[PATCH v6 6/8] KVM: arm64: Add hypervisor overflow stack

From: Kalesh Singh <kaleshsingh@google.com>
Cc: will@kernel.org, maz@kernel.org, qperret@google.com,
	tabba@google.com,  surenb@google.com, kernel-team@android.com,
	 Kalesh Singh <kaleshsingh@google.com>,
	James Morse <james.morse@arm.com>,
	 Alexandru Elisei <alexandru.elisei@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	 Catalin Marinas <catalin.marinas@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Mark Brown <broonie@kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	 Peter Collingbourne <pcc@google.com>,
	"Madhavan T. Venkataraman" <madvenka@linux.microsoft.com>,
	 Andrew Walbran <qwandor@google.com>,
	Andrew Scull <ascull@google.com>,
	 Andrew Jones <drjones@redhat.com>,
	linux-arm-kernel@lists.infradead.org,
	 kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org
Subject: [PATCH v6 6/8] KVM: arm64: Add hypervisor overflow stack
Date: Mon, 14 Mar 2022 13:01:15 -0700	[thread overview]
Message-ID: <20220314200148.2695206-7-kaleshsingh@google.com> (raw)
In-Reply-To: <20220314200148.2695206-1-kaleshsingh@google.com>

Allocate and switch to 16-byte aligned secondary stack on overflow. This
provides us stack space to better handle overflows; and is used in
a subsequent patch to dump the hypervisor stacktrace. The overflow stack
is only allocated if CONFIG_NVHE_EL2_DEBUG is enabled, as hypervisor
stacktraces is a debug feature dependent on CONFIG_NVHE_EL2_DEBUG.

Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
---

Changes in v4:
  - Update comment to clarify resetting the SP to the top of the stack
    only happens if CONFIG_NVHE_EL2_DEBUG is disabled, per Fuad


 arch/arm64/kvm/hyp/nvhe/host.S   | 11 ++++++++---
 arch/arm64/kvm/hyp/nvhe/switch.c |  5 +++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/host.S b/arch/arm64/kvm/hyp/nvhe/host.S
index be6d844279b1..a0c4b4f1549f 100644
--- a/arch/arm64/kvm/hyp/nvhe/host.S
+++ b/arch/arm64/kvm/hyp/nvhe/host.S
@@ -179,13 +179,18 @@ SYM_FUNC_END(__host_hvc)
 	b	hyp_panic
 
 .L__hyp_sp_overflow\@:
+#ifdef CONFIG_NVHE_EL2_DEBUG
+	/* Switch to the overflow stack */
+	adr_this_cpu sp, hyp_overflow_stack + PAGE_SIZE, x0
+#else
 	/*
-	 * Reset SP to the top of the stack, to allow handling the hyp_panic.
-	 * This corrupts the stack but is ok, since we won't be attempting
-	 * any unwinding here.
+	 * If !CONFIG_NVHE_EL2_DEBUG, reset SP to the top of the stack, to
+	 * allow handling the hyp_panic. This corrupts the stack but is ok,
+	 * since we won't be attempting any unwinding here.
 	 */
 	ldr_this_cpu	x0, kvm_init_params + NVHE_INIT_STACK_HYP_VA, x1
 	mov	sp, x0
+#endif
 
 	bl	hyp_panic_bad_stack
 	ASM_BUG()
diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
index 703a5d3f611b..efc20273a352 100644
--- a/arch/arm64/kvm/hyp/nvhe/switch.c
+++ b/arch/arm64/kvm/hyp/nvhe/switch.c
@@ -34,6 +34,11 @@ DEFINE_PER_CPU(struct kvm_host_data, kvm_host_data);
 DEFINE_PER_CPU(struct kvm_cpu_context, kvm_hyp_ctxt);
 DEFINE_PER_CPU(unsigned long, kvm_hyp_vector);
 
+#ifdef CONFIG_NVHE_EL2_DEBUG
+DEFINE_PER_CPU(unsigned long [PAGE_SIZE/sizeof(long)], hyp_overflow_stack)
+	__aligned(16);
+#endif
+
 static void __activate_traps(struct kvm_vcpu *vcpu)
 {
 	u64 val;
-- 
2.35.1.723.g4982287a31-goog


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